Retroreflective sheetings, especially microsphere-based versions, are well known and have been widely used for safety purposes, such as warning signs on vehicles or hazard warnings on roadways, and for information purposes, such as traffic control.
Retroreflective sheetings have also been applied to such articles as tire sidewalls, fabrics, and personal articles such as clothing. For instance, U.S. Pat. Nos. 3,382,908 (Palmquist et al.) and 3,449,201 (Palmquist et al.) disclose the application of strips of retroreflective material to the sidewalls of tires. These patents disclose sheet materials comprising an elastomeric support layer with a monolayer of retroreflective elements embedded therein. In such sheetings, the support layer or at least a back stratum thereof is a vulcanizable elastomer which is compatible with the elastomer of the tire side wall. The support layer typically functions to hold the microspheres in desired monolayer arrangement and in desired uniform alignment. In many instances, the support layer provides a major part, if not essentially all, of the body or strength, e.g., tensile strength, needed to enable the sheeting to be handled during at least the latter steps of its fabrication and conversion, e.g., slitting into strips of desired dimension, as well as during the fabrication of the finished tire. Accordingly, the support layer is typically made somewhate thicker, i.e., typically at least about 6 to about 8 mils (150 and 200 microns) in a sheeting having an overall thickness of between about 8 and about 10 mils (200 and 250 microns), than is necessary to merely hold the microspheres in monolayer arrangement and in desired alignment on the finished tire. Such increased thickness tends to increase the cost of the retroreflective sheeting and in many instances the polymeric material used in the support layer is the costliest component of the sheeting. Furthermore, when such sheetings are incorporated into a rubber article as disclosed in the aforementioned U.S. Pat. Nos. 3,382,908 and 3,449,201, the great thickness of the retroreflective sheeting may tend to weaken the article by displacing a substantial portion of the elastomer, such as in the side wall of a bicycle tire wherein the rubber may be only about 30 mils thick (750 microns).
In other instances, when the support layer is made very thin, the retroreflective sheet material may tend to have such a low breaking force that it is easily broken when subjected to the tensile forces encountered during fabrication or conversion, or when being handled during fabrication of the rubber article, particularly after being cut into strip form.